Lila: Change Arena pairing

[SVVredeburg]

As suggested in https://lichess.org/forum/lichess-feedback/swiss-tournaments-5?page=3#26 and https://lichess.org/forum/lichess-feedback/pairings-in-tournament-arena-four-times-in-series-the-same-player#1. It would be an improvement for Arena tournaments (especially with < 30 players) if in the pairing it is prohibited to play an opponent twice or more consecutively without playing against another one in between. It seems to be the consensus that waiting a little bit longer for a different opponent is preferred. Different than issue #6259

[ornicar]

done

[davidssmith]

Where is the code that addresses this? I'm curious about how the pairing algorithm works.

[pvsmpraveen]

Even I'm curious, can we add the solution / commit to the issues before closing it will be very useful to even contribute :)

[ornicar]

https://github.com/ornicar/lila/commit/b6c1132cea6ee2f6e14d4c00bb94504282e50301